Quiet overload circuit breaker



April 22, 1952 J. D. WOOD QUIET OVERLOAD CIRCUIT BREAKER v 3 Sheets-Sheet 1 Filed March 16, 1948 WO- vyw M ATTORNEYS.

April 22, 1952 J- D. WOOD QUIET OVERLOAD CIRCUIT BREAKER a Sheets- Sheet 2 Filed March 16, 1948 INVENTQR. you w: l). Yz/wc/ BY 1 WK v Zm ATTORNEYS.

April 22, 1952 WOOD 2,594,107

QUIET OVERLOAD CIRCUIT BREAKER Filed March 16, 1948 s Sheets-Sheet 3 I if 3 INVENTOR. 9011 21: 1). Z/av-d BY wr /C v -41m ATTORNEYS.

Patented Apr. 22, 1952 QUIET OVERLOAD CIRCUIT BREAKER Joseph D. Wood, Upper Darby, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa, a cerporation of Pennsylvania Application March 16, 1948, Serial No. 15,182

2 Claims. 1

My invention relates to a novel overload magnet, and more particularly relates to overload magnets used in connection with circuit breakers on alternating current systems.

It is the present commercial practice in overload magnets for controlling the tripping mechanism of a D. C. circuit breaker to provide a normal gap between the armature and its pole face when the armature is against its back stop of a distance such that the armature is attracted at 100% overload in order to effect a tripping operation. Inasmuch as the user of the circuit breaker may, however, wish to increase the value at which the armature responds to fault conditions to say, 200% of the circuit breaker capacity, the armature is biased against its back stop by a spring whose tension may be adjusted by varying amounts so that the armature may be caused to respond to circuit conditions varying from 100% overload to 200% overload as desired by the user.

When it is attempted to use such a magnet on alternating current breakers, it is found that undesirable chatter is set up as the current to the magnet exceeds 100% overload. Assume for example the biasing spring is set for 150% overload. This setting is such that when the instantaneous current value below the peak in a cycle reaches 150% overload, the armature starts to move toward its pole face. The increase in current plus the decrease in air gap as the armature moves toward its pole face is sufiicient to overcome the increased spring tension and the armature is brought up against the pole face to effect tripping operation.

When, however, the current is at some value below this setting, the current may reach values up to the peak of-the cycle which are sufficient to start attracting the armature toward its pole iace. Before the armature reaches the pole face, the current decreases in the cycle at a faster rate than the reduction of air gap reluctance. The M. M. F. decreases faster than the increase in sprin tension.

Accordingly the spring pulls the armature back against its back stop. Thus the armature tends to chatter throughout the period while such a condition obtains and this is mechanically harmful to the overload magnet.

In accordance with my invention I set my armature to effect tripping operation in response to peak current values. To this end I propose to provide an armature for the tripping magnet in which the usual variable tension biasing spring is replaced by a constantbias in which the factor of the bias is a fixed value for all positions of the armature from its back position to the position where it engages the trip mechanism of the circuit breaker.

As has been the practice heretofore, the air gap is calibrated to pick up at the minimum or low rating. In order, however, to permit adjustments to provide armature pick-up at higher than minimum ratings, I add a weight to the armature which effectively biases it against its back stop, the weight being such as to provide the maximum calibration value desired, as for example 200% overload. This Weight provides a constant bias to the armature at every position thereof. The weight is then counterbalanced by a compression spring permitting adjustment between the high and low setting values.

Accordingly an object of my invention is to provide a novel trip magnet for alternating current circuit breakers enabling adjustments at the field of use which will cause the electromagnet to respond to currents from any desired minimum to any desired maximum overload without chatter.

A further object of my invention is to provide a novel trip magnet which is arranged to respond to peak currents in a cycle.

There are other objects of my invention which, together with the foregoing, will become apparent in the detailed description which follows, and the drawings in which Figure 1 shows my novel device as applied to an alternating current circuit breaker.

Figure 2 shows the essential elements of my invention with the electromagnet de-energized or energized at a current value below full load.

Figure 3 shows the electromagnet of Figure 2 in energized condition at a current value above full load.

Referring now to Figure 2, the electromagnet H provided with windings l2 and the usual laminated magnetic core I3 has an armature l4 pivotally mounted at 5 about which the armature moves in response to energization of the windings of the electromagnet. With the armature against its back stop, the extension 16 on the armature I4 is spaced form its pol face I? on the magnetic structure of the electromagnet 'by a distance such that at a predetermined the added weight or mass 2| secured in any well known manner, as by riveting, to the armature l4 and having a moment of force in a clockwise direction about the pivot 65.

The added weight 2! is selected of such a value that it holds the armature against movement up to the maximum calibration value. Thus, for example, the spacing between the armature extension I6 and its pole face [1 may be such as to cause the armature without weight 2| to be moved toward the pole face in response to 100% load conditions in the absence of the weight 2|.

However, the weight 2| is of such a value that the armature cannot move toward its pole face until the electromagnet is energized by currents 200% above rating. This then supplies the two limiting values for the operation of the armature.

In order to provide adjustment between these two limiting values, a compression spring 22 is provided mounted between the pan shaped members '23 and 24, the pan 23 forming a back stop for the armature at its weight 2 I An adjusting screw 25 is made adjustable for varying the height of the spring 22. Extending therefrom is a pointer 26 in the guide 2'! and moving across a calibration plate 28, calibrating to show the setting for each value of spring position. The raising and lowering of the spring thus varies the back stop or dropped out position of the armature.

The operation of this device will now be clear. Assume that the screw 25 is adjusted to position the compressed spring and the armature so as to overcome enough of the added weight 2| to permit the projection it to move toward its pole face when 150% overload condition obtains.

This may now be the peak value of current in the cycle since once the armature starts moving, the spring 22 does not offer an increased counterforce but instead continues, although at decreased value, to assist the armature movement toward its pole face. Accordingly this aid plus the decrease in air gap may be made sufficient to overcome the decrease in current through the coils in the immediately following period of the cycle. The armature therefore, once it starts toward its pole face, follows through to complete its tripping operation.

.If its peak current flowing through the winding of the magnet is slightly below this operating value, the armature will beunable to respond and accordingly will not chatter.

As already explained, this response may be adjusted to occur for any range of values between the minimum setting as determined by the spacing of the gap between the pole face I! and the projection it on armature [4 when it is in its back stop position and when the spring 22 has been compressed to provide a complete counterbalance equal to the weight 2|. In this case the armature operates as if no weight, such as 2|, has been added and will respond to 100% overload or any desired minimum setting. The maximum overload condition is obtained when the compressionspring action on the weight 2| has been brought to substantially zero.

In this case the weight 2| is fully effective to prevent armature movement until current corresponding to 200% or whatever desired maximum current rating is desired flows through the magnet windings. Here again since there is no increasing counterbiasing action, oncev the arma- ,ture starts movement toward its pole race, the

decrease in air gap is more than suificient to overcome the decrease in winding current, Ineach case th'e'conipres'sion spring as distinguished from the tension spring of the prior art does not function once the armature starts to move toward its pole face to oppose this action and accordingly the setting of the compression spring can be such that the armature will not respond to any value below the desired rating and will become instantly responsive at that rating.

Thus in Figure 3 with the armature pulled to engage the pole face at which position the trip bar 29 has been engaged to effect a tripping operation, the compression spring has assisted as shown in the movement of the armature to its fully engaged position. This is in distinction from the tension spring of the prior art which when adjusted to the desired value of the rate of overload desired increases its tension as the armature moves toward its pole face and thus functions to restore the armature to its back position the instant the current in a cycle passes below its maximum value.

In Figure l, I have shown my novel overload magnet as applied to a circuit breaker although it will be understood that any circuit breaker in an alternating our system may be employed. Here I have shown the usual panel board 3| having upper and lower terminals 32 and 33 which pass through openings in the board 31 and are suitabiy insulated therefrom on supporting brackets 3 The lower terminal 38 is electrically connected to the windings of the magnet Hand thence extends over the conductor 36 to the pigtail 3'. connected to the movable contact arm 38.

Contact arm is provided with a contact which engages the fixed contact 39 which in turn is connected to the upper terminal 32. Contact arm 33 is movably mounted for rotation on the shaft i! under control of the trip mechanism of the overload magnet ii, the closing magnet 48 and the manual closing means 43 in a manner shown and described in detail in Patent No. 2,390,735.

Although I have shown my invention as applied to a specific circuit breaker, it will be obvious that this is only by wa or" illustration of one of its uses. Moreover, although I have shown the mass or weight 2i in a broad relation to the armature it will be apparent to those skilled in the art that this weight may be other wise distributed on the armature or may be an integral part of the, armature and still come within the spirit of my invention, and I do not wish to be limited except as set forth in the appended claims.

I claim:

1. A circuit breaker for alternating currents comprising a frame and an electromagnet mounted on said frame and having a pole face, a pivoted armature having an end movable toward said pole face, means biasing the armature away from said pole face consisting of weight means acting on said armature and tending to bias it so as to maintain said end away from said pole face, said weight means being disposed so as to maintain a substantially uniform biasing force in all operating positions of said armature, said weight means having a mass value such as to maintain said armature from being activated by said electromagnet except at a predetermined maximum peak current, a backstop against which said armature is'biased by said weight means, said backstop comprisinga spring' carried by the frarneand disposed to engage the armature and to oppose the biasing effect of said weight means, and means for adjusting the position of said spring relative to said frame for varying the dropped out position of the armature, whereby said circuit breaker may be set. by adjusting said spring position to trip at values ranging from a minimum to said aforementioned maximum, and wherein said spring expands when said armature end is moving towards said pole face to assist in overcoming the biasing effect of said weight means.

2. A circuit breaker as set forth in claim 1, wherein said armature is disposed to pivot in a vertical plane and wherein said weight means comprises an element carried by and integral with said armature and extending therefrom in a substantially horizontal direction, the center of gravity of said element being approximately in the horizontal plane of the pivotal axis of said armature, and said spring being disposed to act directly against said element.

JOSEPH D. WOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 276,565 Daft 1, 1883 276,567 Daft May 1, 1.883 593,481 Lowrie Nov. 9, 1897 1,103,530 Newburn M July 14, 1914 1,479,834 Reynolds Jan. 8, 1924 1,741,409 Dunn Dec. 31, 1929 2,419,892 Graves, Jr. Apr. 29, 1947 2,426,068 Taliaferro Aug. 10, 1947 FOREIGN PATENTS Number Country Date 130,207 Great Britain July 31, 1919 225,739 Great Britain Dec. 8, 1924 

